Spinning porous membrane separators have been used to separate plasma from cellular components of whole blood. A well-known plasmapheresis device is the Plasmacell-C separator sold by Fenwal, Inc. of Lake Zurich, Ill. A detailed description of a spinning membrane separator may be found in U.S. Pat. No. 5,194,145 to Schoendorfer, which is incorporated by reference herein. This patent describes a membrane-covered spinner having an interior collection system disposed within a stationary shell. Blood is fed into an annular space or gap between the spinner and the shell. The blood moves along the longitudinal axis of the shell toward an exit region, with plasma passing through the membrane and out of the shell into a collection bag. The remaining blood components move to the exit region between the spinner and the shell and then are typically returned to the donor.
Spinning membrane separators have been found to provide excellent filtration rates, due primarily to the unique flow patterns (“Taylor vortices”) induced in the gap between the spinning membrane and the shell. The Taylor vortices help to sweep the surface of the membrane to inhibit the cellular components, primarily red blood cells, from depositing on and fouling or clogging the membrane.
In membrane filtration, the identity of the filtrate is dependent primarily on size differentiation between the nominal pore size of the membrane and the cellular components of the retentate. For performing plasmapheresis by means of a spinning membrane, the nominal pore size is typically on the order of 0.65 μm, which allows plasma to pass through the membrane while retaining the bulk of the cellular blood components, namely white blood cells (“WBCs”), red blood cells (“RBCs”) and platelets (“PLTs”). This retentate remains in the gap between the spinning membrane and the housing, and then exits the spinner housing. Thus, separation of WBCs, RBCs and PLTs from each other would require passing the retentate again through a separation device in which the membrane has a different nominal pore size, e.g., 4.0-5.0 μm, which would permit RBCs to pass through, but retain WBCs.
By way of the present disclosure, methods are provided for separating the various blood components using a spinning membrane separator in which the type of cell that is separated is not solely dependent upon the nominal pore size of the membrane. Consequently, different resultant cell products may be obtained using a single spinning membrane separator.